Known as one of techniques for directly producing a strip from molten metal is twin-roll continuous casting where molten metal is supplied to between a pair of rotated rolls to deliver a solidified metal strip.
FIGS. 1 and 2 show a continuous casting machine with conventional casting rolls, each casting roll comprising a cylindrical roll body 2 on which side weirs 1 abut, and hollow stub axles 3 fitted into opposite ends of the roll body 2, respectively (see, for example, Patent Literature 1).
The roll body 2 is shaped such that the opposite ends have an outer diameter smaller than that of an intermediate portion. The side weirs 1 abut on end surfaces of the lager-diameter intermediate portion.
The roll body 2 is formed with a plurality of longitudinal cooling passages 4 located circumferentially equidistantly and extending axially of the roll body, and a plurality of radial cooling passages 5 extending radially of an roll axis and communicating with corresponding ends of the longitudinal passages 4, respectively.
The longitudinal passage 4 passes through the roll from a portion of one of the end surfaces of the roll on which one of the side weirs 1 does not abut to a portion of the other end of the roll on which the other side weir 1 does not abut. Fitted into each end of the longitudinal passage is a plug 6 or a bolt 7 serving as plug to connect the stub axle 3 to the roll body 2.
The radial passage 5 passes from an inner periphery of the roll near end of the roll, at a right angle, into the longitudinal cooling passage 4.
The stub axles 3 is formed with radial cooling passages 8 such that cooling water W continuously flows through one of the radial passages 5 with which the longitudinal passage 4 communicates, the longitudinal passage 4 and the other radial passage 5 with which the same longitudinal passage 4 communicates, in the order named. For the radial passages 8, for example, a rotary joint is incorporated.
The continuous casting machine comprises the paired casting rolls each constituted by the above-mentioned roll body 2 and stab axles 3. The rolls are horizontally juxtaposed such that a nip between the rolls is adjusted to be increased/decreased depending on thickness of a strip S to be produced. The side weirs 1 surface-contact one and the other end surfaces of the larger-diameter intermediate portions of the roll body 2, respectively.
Rotational directions and velocities of the casting rolls are set such that respective outer peripheries of the rolls are moved from above toward the nip G at constant velocity.
In the continuous casting machine, molten metal is poured into space defined by the side weirs 1 and roll bodies 2 to provide molten metal pool M while heat is removed from the roll body 2 by flow of cooling water W through the radial and longitudinal passages 5 and 4. With the casting rolls rotated, metal is cooled on the outer peripheries of the roll bodies 2 into solidified shells, a resultant strip S being delivered from the nip downward.
At so-called triple point regions where the roll body 2, the side weir 1 and the molten metal pool M meet, the solidified shell may be extraordinarily produced.
Any solidified shell produced at the triple point region may be dragged and peeled by the solidified shell formed on the outer periphery of the roll body 2 and may be bitten at the nip, which brings about not only defective shape of the locally thickened strip S but also flaring or expansion of the nip due to the defective portion of the strip, resulting in reduction in cooling efficiency, fracture of the strip S due to reheating from the molten metal and damage on the side weirs 1 upon drop-out of the solidified shell.
In order to overcome these, it has been proposed a continuous casting machine in which molten metal is directed to the side weirs 1 and is aggressively poured tangentially of the roll bodies 2 to prevent unnecessary solidified shells from being produced at the triple point regions (see, for example, Patent Literature 2).
In the above technique, the hot molten metal just poured may pass along the side weirs 1 to reach the nip within an extremely short time, resulting in scrimpy thickness of the solidified shell at axial end vicinities of the roll body 2 especially upon production of strip S with thickness of the order of 2 mm.
[Patent Literature 1] JP 11-314138A
[Patent Literature 2] JP 62-45456A